Connectivity and voice quality are key reliability issues in today's VoIP (voice over Internet Protocol) networks. Today's VoIP users increasingly expect the Quality of Service (QoS) of the call to be equal or close to that of the Public Switched Telephone Network (PSTN). Because network conditions may change rapidly and continuously, connectivity for a VoIP call cannot be guaranteed. Further, problems that may be commonly encountered in an IP network such as packet loss, packet delay, and out of order packet delivery may lead to deteriorating quality of VoIP voice calls.
Unlike data connections, a real-time application like voice calls place much stricter requirements on packet delivery sequence and timing. Significant packet loss, packet delay, and out of order delivery problems make telephone conversations difficult. Users may experience echoes and talker overlap that are perceived as significant indicators of inferior QoS.